In the aforementioned U.S. Pat. No. 4,975,230, I have explained that reticulate metal structures have been generated heretofore for many purposes. For example, such structures may provide a conductive network suitable for use as supports in batteries in which an active material is applied to and held in place by the support, or is formed on the support. Porous structures of this type may also be used as sieves, screens or the like. They may be utilized as catalyst materials and can promote reaction between various phases. In general, they have been characterized by a relatively high surface area per unit volume or weight of the support.
Prior to the method described in U.S. Pat. No. 4,975,230, such materials were produced in a variety of ways. These include chemical vapor deposition, electroless deposition and even electrodeposition on fibrous supports, e.g. nonwoven or needled fabrics. The fibrous support could be destroyed by pyrolysis to leave the reticulate metal structure.
It has been pointed out in the last mentioned copending application, moreover, that these systems had a variety of drawbacks and that, by and large, the systems were not capable of providing the large number of sharp edged or angled surfaces or irregularities that were desirable, especially where specific activity was a main function of the structure made.
In the aforementioned U.S. Pat. No. 4,975,230, therefore, I describe a method utilizing arc vapor deposition for fabricating such structures, especially of metal, that high porosity and, especially, a continuum of the reticulated metal phase and a continuum of the openwork could be obtained, utilizing as a support a foam structure which was pyrolyzable.
Essentially, the method of that application made a reticulate structure by applying to a pyrolyzable openwork substrate, preferably a pyrolyzable foam of a synthetic resin material, by low-temperature arc vapor deposition, a coating of at least one material which was generally a metal but could also be a semiconductor or a ceramic. The coating which is thus formed on the substrate forms an openwork structure which, upon pyrolysis, continues to be an openwork structure.
The coated product, therefore, was subjected to pyrolysis to destroy the synthetic resin support and form a reticulate structure of the metal, for example, which could then be sintered to provide a mechanically stable and coherent, highly porous and branched structure with irregular surfaces.
In the low-temperature arc vapor deposition process there described, which was similar to that set forth in the earlier copending application and patents, the rate of deposition of the metal or other material is a function of the rate at which the material is deposited from the vapor state onto the substrate. While this rate may vary from metal to metal or material to material, it is nevertheless comparatively slow and it is not unusual in depositing 60 grams per square foot on and in the foam synthetic resin for the deposition period to require say 100 hours and even more.